1. Field of the Invention
The present invention relates to a method of piecing a yarn in an open-end spinning machine.
2. Description of the Prior Art
Open-end spinning machines generally operate by allowing a spun yarn from a spinning unit to pass between a draw-off roller and a presser roller, and to be wound around a bobbin positively rotated by a take-up drum while traversing the yarn across the bobbin for forming a package. When the yarn being spun is broken for some reason, a yarn piecing machine is moved toward and stopped in front of the spinning unit where the yarn breakage has occurred, for piecing the yarn.
Variations in the time (hereinafter referred to as a "yarn piecing machine arrival time") which is unavoidable for the yarn piecing machine to reach the spinning unit for yarn piecing have caused the following problems: when a yarn breakage occurs, the feed roller of the spinning unit is stopped to stop a sliver while the latter is being sandwiched between the feed roller and a presser. Since a spinning rotor and a combing roller are idly rotated continuously unless the spinning unit is opened for cleaning by an opening mechanism mounted on the yarn piecing machine, the end of the sliver is gradually scraped off by needles of the combing roller. The variations in the yarn piecing machine arrival time result in different shapes (fiber quantities) of sliver ends. It is necessary to start supplying the sliver by starting the feed roller immediately prior to arrival of the broken yarn end at a fiber collecting surface of the spinning rotor so that when the broken yarn end as inserted in a withdrawal tube of the spinning unit reaches the fiber collecting surface, the fibers also reach the fiber collecting surface at the same time or an earlier time. Experiments have shown that where the pre-feed time between the time of starting the feed roller and the time of arrival of the yarn end at the fiber collecting surface is constant, the timing for the fibers to reach the fiber collecting surface and the shape in which the fibers are deposited on the fiber collecting surface vary dependent on the quantity of the fibers at the sliver end, resulting in different rates of successful yarn piecing.
According to a conventional yarn piecing method, the package is rotated in a reverse direction by a rewinding package-driving roller mounted on the yarn piecing machine to feed the broken yarn end through the withdrawal tube onto the yarn collecting surface in the spinning rotor. When the yarn end is joined to the fibers on the yarn collecting surface, the package is rotated in a normal direction to pull up the yarn. In synchronism with the starting of reverse rotation of the rewinding roller, the sliver supply feed roller in the spinning unit is actuated to supply the fibers into the spinning rotor.
With the above yarn piecing method, the sliver starts being fed by the feed roller at the same time that the rewinding roller starts to rotate in the reverse direction. For adjusting the timing for the broken yarn end to reach the fiber collecting surface of the spinning rotor and also the timing for the fibers loosened by the combing roller to reach the fiber collecting surface at the time when a different yarn number count is employed, it is required to change the speed at which the rewinding roller is to be reversed. This varies the speed at which the yarn is inserted into the withdrawal tube dependent on the yarn number count. Accordingly, the yarn insertion speed becomes inappropriate, so that the yarn may not be inserted properly and may fail to progress in the withdrawal tube, resulting in a reduced rate of successful yarn piecing.
According to the prior yarn piecing process, the package is reversed by a drive roller in the yarn piecing machine to rewind the yarn from the package, and the yarn is gripped by a pair of yarn grip rollers while the yarn end is cut off into a predetermined length. The yarn end is then moved directly above the withdrawal tube in the spinning unit, and thereafter the package and the yarn grip rollers are reversed to insert the yarn into the withdrawal tube. When the yarn end is moved onto the fiber collecting surface and gets pieced, the package and the yarn grip rollers are rotated in the normal direction to draw the yarn out of the withdrawal tube. The yarn is released from the yarn grip rollers and transferred between the draw-off roller and the presser roller. The package is separated off the drive roller and rotated by the take-up drum in the spinning machine for normal spinning operation.
The foregoing conventional yarn piecing process is disadvantageous in that when the yarn spinning speed varies due to a different yarn number count employed, the RPMs of the yarn grip rollers and package drive roller in the yarn piecing machine at the time of yarn withdrawal have to be changed to meet the speed of operation of the spinning machine, requiring high-precision controls which make the entire apparatus complex and costly.
In open-end spinning machines, the RPMs of the rotor, draw-off roller, and take-up drum are preset in a fixed relationship to achieve a predetermined spinning speed dependent on a desired yarn number count and number of twists. The rollers and drum are normally powered by a common drive source. With the above-mentioned prior yarn piecing process, the pieced yarn from the spinning unit is withdrawn by the yarn withdrawal mechanism (the rewinding roller and yarn grip rollers) in the yarn piecing machine. The rollers in the yarn piecing machine are powered by a drive source different from the drive source on the spinning machine base. Therefore, the RPMs of the rollers in the yarn piecing machine do not necessarily synchronize with the spinning speed of the rotor, with the result that the spun yarn may be subjected to variations in thickness and twist, and may be poor in quality. According to another yarn piecing method, the RPM of the rotor is reduced for piecing a yarn at a low speed, and the yarn is withdrawn by the yarn withdrawal mechanism in the yarn piecing machine. After the rotor and the yarn withdrawal mechanism have reached a normal high RPM, the yarn is transferred to the draw-off roller on the machine base. However, the yarn piecing process has had the drawback in that the rate of production is lowered during the time required for the rotor and mechanism to reach the high normal speed from the low speed. Another problem is that the rotor, the combing roller, and the feed roller for a spinning unit with a yarn breakage must be driven by an external drive source different from the drive source on the machine base, so that the entire mechanism is complicated and expensive.